Conventionally, in a charger for charging, for example, a lead storage battery, or a load to which power is supplied from a battery, a circuit for preventing inrush current is provided between the battery and a device connected to the battery. This circuit functions to prevent damage to the contact portion of a plug due to inrush current or sparks generated by a voltage difference between the charger or a capacitor for removing a high frequency component and the battery in connection between the battery and the charger or between the battery and the load, the capacitor being connected in parallel with the road.
The above conventional circuit for preventing inrush current is described below with reference to the drawings.
As a conventional technique (for example, see Patent Document 1), FIG. 6 is a circuit diagram of the conventional circuit for preventing inrush current in which power is supplied from a battery 1 via a contact portion including plugs 3a and 3b to a load F1 across which an electrolytic capacitor 7 is connected in parallel. The plugs 3a and 3b of the contact portion are detachably connected.
Resistors 2a and 2b are always connected in parallel to the plugs 3a and 3b of the contact portion as shown in FIG. 6. Even if the plugs 3a and 3b of the contact portion are not connected, the battery 1 continuously charges the electrolytic capacitor 7 via the resistors 2a and 2b to eliminate a voltage difference between the battery 1 and the electrolytic capacitor 7. This prevents inrush current generated when the plugs 3a and 3b of the contact portion are connected.
Further, as shown in FIG. 7, there is a technique in which a resistor 2c and a switch 5a that causes a short circuit in the resistor 2c are provided between the plugs 3a and 3b and the electrolytic capacitor 7 connected in parallel across the load F1. In this technique, when the plugs 3a and 3b are connected, the electrolytic capacitor 7 is charged via the resistor 2c, and after the electrolytic capacitor 7 is charged, the switch 5a is closed to cause a short circuit in the resistor 2c. 
Moreover, there is another conventional technique (for example, see Patent Document 2). In this technique, as shown in FIG. 8, a closed magnetic circuit coil 6 is provided between a battery 1 and an electrolytic capacitor 7 to suppress an abrupt change in current by the inductance component of the coil 6, and prevent inrush current when a switch 5b is closed with a large voltage difference between the battery 1 and the electrolytic capacitor 7.